1. Field of the Invention
The present invention relates to a film bulk acoustic resonator (hereinafter, referred to as an FBAR), and more particularly to a method for manufacturing a wafer level package type FBAR device, which can achieve miniaturization and reduction of a manufacturing cost due to a simplified process.
2. Description of the Related Art
In recent years, wireless communication devices have tended to become much leaner, and enhanced and diversified in their quality and functions due to the development of the communication industry. This recent trend sincerely requires miniaturization and enhancement in quality related with various elements for use in the wireless communication devices. Nowadays, therefore, chip shaped elements have become increasingly commercialized.
The wireless communication devices essentially utilize a voltage controlled oscillator (VCO), a filter, a duplexer and other devices, and these devices basically contain at least one resonator. Such a resonator is used to induce a resonance effect due to the piezoelectric effect thereof. Currently, active development is targeting an FBAR, which is preferable for integration due to its thin film shape, and has good properties.
Typically, the FBAR is formed on a wafer with a piezoelectric layer through a vapor deposition and the like. At the upper and lower surfaces of the piezoelectric layer are provided upper and lower electrodes, respectively, for applying electricity to the piezoelectric layer so as to oscillate it. In addition to the upper and lower electrodes, a desired air gap is formed at the lower surface of the piezoelectric layer in order to improve a resonance property of the piezoelectric layer. The formed piezoelectric layer and upper and lower electrodes are packaged for the purpose of protection. In this case, a wafer level package (hereinafter, referred to as a WLP) technique may be adopted in order to facilitate mass production and achieve miniaturization due to a simplified packaging process. The WLP technique achieve the manufacture and packaging of the device simultaneously by bonding a cap wafer serving as an upper package, a lower package, and a substrate wafer to one another. The substrate performs a function of a device. FBAR devices manufactured by the WLP technique accompany increases of the number and function of external terminals provided at the outside due to the diversification of their functions, but also accompany a reduction in the size of the package thereof. This makes it difficult to design the shape, size and position of the external terminals.
FIGS. 1A and 1B and 2A and 2B illustrate different structures of conventional FBARs manufactured in accordance with a WLP technique, respectively.
Referring to FIGS. 1A and 1B, one of the conventional FBARs comprises a substrate 11, and a cap 12 disposed on the substrate 11. The substrate 11 is formed with an air gap 11a, a lower electrode 11b, a piezoelectric layer 11c, and an upper electrode lid. The cap 12, made of a wafer, is formed with an empty cavity 12a at a portion where a circuit element is located. The cap 12 is further formed with perforated bores at positions corresponding to the upper and lower electrodes lid and 11b. After bonding the cap 12 to the substrate 11, the perforated bores are filled with a printing metal material, and external electrodes 13 are printed onto the upper surface of the cap 12 through a printing technique so that the external electrodes 13 are electrically connected to the upper and lower electrodes lid and 11b on the substrate 11.
In this case, the formation of the external electrodes 13 requires a printing process of metal electrodes for use as the external electrodes. Further, since the perforated bores have to be formed in the cap 12 in order to achieve electrical connection between the external electrodes 13 and the upper and lower electrodes lid and 11b on the substrate 11, there is a considerable limitation in design of a cap wafer.
Referring to FIGS. 2A and 2B, the other conventional FBAR, which is similar in its basic configuration to that shown in FIG. 1A, comprises the substrate 11, and a cap 15 disposed on the substrate 11. The substrate 11 is formed with the air gap 11a, the lower electrode 11b, the piezoelectric layer 11c, and the upper electrode lid. The cap 15, made of a wafer, is formed with an empty cavity 15a at a portion where a circuit element is located, and further formed with perforated bores 16a at positions corresponding to the upper and lower electrodes lid and 11b. After bonding the cap 15 to the substrate 11, instead of filling a printing metal material into the perforated bores 16a, metal films are formed on the inner surfaces of the perforated bores 16a and on certain portions of the upper surface of the cap 15 adjacent to the perforated bores 16a by performing a metal deposition process in a state wherein the remaining portion of the upper surface of the cap 15, except for certain portions for forming external electrodes 16, is shield by the use of a mask made of a photoresist (PR), metal or glass materials. In this way, the upper and lower electrodes lid and 11b on the substrate 11 are electrically connected with the external electrodes 16, respectively.
In this case, similarly to the previously described case, the formation of the external electrodes 16 requires a perforated bore forming step and a metal deposition process, resulting in a considerable limitation in design of a cap wafer due to the perforated bores.
Although the structures of the conventional FBARs as stated above have been achieved according to most effective methods for miniaturization, due to the previously mentioned various processes including printing, metal deposition and formation of perforated holes, the conventional FBARs requires a relative complex process and have considerable limitations in design of the FBARs. This makes it difficult to secure a profit margin required for mass production and results in a high manufacturing cost.
In addition to the above problems, when it is desired to increase the number of external terminals in existing commercialized products, a photolithography technique has to be applied thus resulting in a further increase of manufacturing costs.